This invention relates to warning and alarm systems and particularly to warning and alarm systems adapted to communicate when a dangerous voltage is present on the third rail of a transit or railroad system. The typical transit system will have two running rails on which the wheels of the cars roll and a third rail which carries the electric power for the electric motors used to drive the transit cars. This voltage which may typically be 600 volts D.C., although specific systems may have substantially different voltages. The maintenance crews performing work in the vicinity of third rails must have the power turned off on the third rail to avoid an intolerably dangerous working condition. The power to the third rail is typically turned on and off from a remote panel which is not visible to the maintenance crew working near or on the rails.